1. Field of the Invention
This invention relates to a technique for printing images on a printing medium by ink injection.
2. Description of the Related Art
In recent years, color printers of the type in which inks of multiple colors are ejected from an ink head have become popular as output devices for computers and are now widely used in processes in which images processed by computers are printed in numerous colors and gradations. Such printers are usually provided with improved print resolution in order to allow text and other line drawings to be printed with good results.
However, improving print resolution is accompanied by an increase in the amount of data being processed. The resulting drawback is that, in particular, considerable time is needed to transfer data between computers and printing apparatus, resulting in reduced printing speed.
Accordingly, an object of the present invention is to smooth the outlines of line drawings while minimizing the reduction in printing speed.
In order to attain the above and the other objects of the present invention, there is provided a printing apparatus capable of selectively forming any of N types of dot recording states which are different in an ink amount and/or in an ink-deposited position in a pixel area on a print medium. N is an integer of 2 at least. The printing apparatus comprises a print head, a receiver, a dot selector, and a drive signal generator. The print head has a plurality of nozzles and a plurality of ejection drive elements for ejecting ink drops from corresponding plurality of nozzles. The receiver is configured to receive print data from an external device, the print data containing gradation data indicative of M values for each pixel in a printed image. M is a positive integer of (Nxe2x88x921) at most. The dot selector is configured to select one type of dot recording state for each pixel from the N types of dot recording states in response to the print data. The selected type of dot recording state is smoothing an outline contained in a printed image. The drive signal generator is configured to generate drive signals for driving the ejection drive elements to form the selected type of dot recording state.
As used herein, the term xe2x80x9cdot recording statexe2x80x9d has a broad meaning that includes states in which dots may or may not be recorded.
The gradation data received by a printing apparatus from an external device has M gradations (where M is an integer of (Nxe2x88x921) or less), so these gradation data alone can only reproduce a maximum of (Nxe2x88x921) dot-forming states. A dot selector selects a recording state from among those having N types of dots on the basis of these gradation data. In the specific case in which the gradation data received from an external device are binary data, the dot selector selects a state in which no dots are formed when the gradation value is zero, and selects a small or large dot when the gradation value is one.
Therefore, the first printing apparatus of the present invention allows images to be reproduced using a greater number of types of dot recording states in comparison with that provided by the gradation data received from an external device. It is therefore possible to smooth image outlines while minimizing the increase in data transmission from the external device.
In the printing apparatus of the present invention, the N types of dot recording states include at least one dot recording state which is identical to another in the ink amount and different in the ink-deposited position.
Therefore, the outlines of line drawings can be smoothed even by using dots created using the same amounts of ink but formed at different locations.
In a preferred embodiment of the invention, a number of bits per pixel in the gradation data is less than a number of bits per pixel in data indicative of the N types of dot recording states.
Adopting this approach makes it possible to minimize the increase in data transmission from an external device.
In a preferred embodiment of the invention, the dot selector is configured to select one dot recording state for each pixel to smooth an outline contained in the printed image based on a gradation value of the each pixel and a gradation value of a pixel adjacent to the each pixel according to the gradation data.
With this approach, the dot type can be selected with consideration for the gradation values of pixels adjacent to each pixel, making it possible to easily minimize the jaggies commonly developed by line drawings.
In a preferred embodiment of the invention, the drive signal generator comprises an original drive signal generator and an original drive signal shaper. The original drive signal generator is configured to generate an original drive signal having a plurality of pulses within a main scan period for a single pixel. The original drive signal is commonly applicable to the plurality of ejection drive elements. The original drive signal shaper is configured to shape the original drive signal with a masking signal to generate the drive signal. The drive signal is configured to represent any of the N types of dot recording states. The original drive signal shaper comprises a mask pattern storage, a mask pattern selector, a masking signal generation circuit, and a masking unit. The mask pattern storage is configured to store a plurality of mask patterns. Each mask pattern contains a plurality of types of original masking signal data to be used for generating the masking signal. The mask pattern selector is configured to select one mask pattern from the plurality of mask patterns in response to the selection of the dot recording state. The selected mask pattern is capable of reproducing the selected dot recording state. The masking signal generation circuit is configured to select one original masking signal data from the plurality of types of original masking signal data contained in the selected mask pattern in response to the selection of the dot recording state, and also to generate the masking signal with the selected original masking signal data. The masking unit is configured to selectively mask the plurality of pulses in the original drive signals with the masking signals, to thereby generate the drive signal provided to the each ejection drive element.
With this approach, a printing apparatus in which mask patterns are used to control dot size can be employed with ease.
In a second embodiment, there is provided a printing apparatus capable of selectively forming any of N types of dot recording states which are different in an ink amount and/or in an ink-deposited position in a pixel area on a print medium. N is an integer of 2 at least. The printing apparatus comprises a print head, a receiver, a dot selector, a font processor, and a drive signal generator. The print head has a plurality of nozzles and a plurality of ejection drive elements for ejecting ink drops from corresponding plurality of nozzles. The receiver is configured to receive print data from an external device. The print data contains text-specifying data for specifying at least a text to be recorded and gradation data indicative of a gradation value of each of first pixels in a printed image other than text. The dot selector is configured to select one type of dot recording state from the N types of dot recording states in response to the print data. The selected type of dot recording state is to be recorded for each of the first pixels. The font processor is configured to store a scalable font data and also to define gradation values of each of second pixels in response to the text-specifying information and the scalable font data. The second pixels are corresponding to a higher resolution than that of the gradation data. The scalable font data contains data indicative of a text shape in a form of vector information. The drive signal generator is configured to generate drive signals for driving the ejection drive elements to form the selected type of dot recording state. The dot selector selects one type of dot recording state from the N types of dot recording states in response to an arrangement of gradation values of the second pixels within the first pixel. The selected type of dot recording state is best suited for expressing the arrangement of the gradation values.
According to the second embodiment of the present invention, gradation values are established for a second pixel with a higher resolution than that afforded by the gradation data in accordance with text-specifying information, and dots are selected such that their configuration is best suited for expressing the manner in which the gradation data of gradation values are arranged within the first pixels, making it possible to print smoothly outlined texts. As a result, it is possible to smooth text outlines while minimizing the increase in print data when, for example, mixed images consisting of text and natural images are printed.
In a preferred embodiment of the invention, the drive signal generator comprises an original drive signal generator and an original drive signal shaper. The original drive signal generator is configured to generate an original drive signal having P pulses within the main scan period of a single pixel. P is an integer of 2 at least. The original drive signal is commonly applicable to the plurality of ejection drive elements. The original drive signal shaper is configured to shape the original drive signal with a masking signal, thereby generating drive signals configured to represent any of 2P kinds of dot recording states. 2P denotes the P-th power of 2. The font processor defines the gradation values in the second pixels corresponding to a resolution. The resolution is P times as greater as a resolution of the gradation data. The original drive signal shaper comprises a mask pattern storage, a mask pattern selector, a masking signal generation circuit, and a masking unit. The mask pattern storage is configured to store a plurality of mask patterns. Each mask pattern containing a plurality of types of original masking signal data to be used for generating the masking signals. The mask pattern selector is configured to select one mask pattern from the plurality of mask patterns in response to the selected type of dot recording state. The selected mask pattern is capable of reproducing the selected type of dot recording state. The masking signal generation circuit is configured to select one type of original masking signal data from the plurality of types of original masking signal data contained in the selected mask pattern in response to the selected type of dot recording state, and also to generate the masking signal with the selected type of original masking signal data. The masking unit is configured to selectively mask the P pulses in the original drive signals with the masking signals, to thereby generate the drive signal provided to the each ejection drive element.
Adopting this approach allows resolution to be substantially enhanced in the direction of main scanning in the case of text expression alone, making it possible, for example, to print text alone (for which resolution has priority over the number of gradations) with high resolution and at the same time to print natural images (for which the number of gradations has priority over resolution) when, for example, the natural images are printed as mixed images.
In a preferred embodiment, the printing apparatus comprises a main body and a carriage. The main body is of the printing apparatus. The carriage is configured to move in a main scan direction, and also to carry the print head, the masking signal generator, and the masking unit. The printing apparatus transmits data for the mask pattern selection and data for the original masking signal selection from the main body to the carriage in parallel.
An advantage of this approach is that the reduction in printing speed that accompanies an increase in the volume of data in the printing apparatus can be minimized because less time is needed to transfer print signals to the print head.
In a preferred embodiment of the invention, the printing apparatus has a bidirectional printing function for printing during both forward and return passes of main scan, and stores the plurality of mask patterns in the mask pattern storage. The plurality of mask patterns are stored such that reversed original masking signal data are selected for forward and return passes, respectively.
An advantage of this approach is that a smoothly outlined text can be expressed even when bidirectional printing is performed.
According to a preferred embodiment, integer N is 2 or 3, and integer M is 2.
In a third embodiment, there is provided a printing apparatus for printing by ejecting ink drops from a print head to form dots. The apparatus comprises a print mode selector and a smoothing processor. The a print mode selector allows a user to select one of a plurality of print modes including a specific text print mode suitable for printing text documents, and a photographic print mode suitable for printing photographic images. The smoothing processor is configured to perform a smoothing process in order to smooth an outline contained in a printed image when the specific text print mode is selected, and also to dispense with the smoothing process when the photographic print mode is selected.
According to the third embodiment of the present invention, a smoothing process is carried out only when a specific text print mode is selected in accordance with the printing mode specified by the user, making it possible, for example, to achieve a result in which performing the smoothing process allows the outlines of printed images to be smoothed by this routine during printing while preventing the picture quality of photographs from being degraded.
In a preferred embodiment of the invention, the printing apparatus further comprises a print head driver and a print data generator. The print head driver configured to form any of N types of dots selectively with each nozzle. The N types of dots is different in size in a single pixel area on a print medium. N is an integer of 2 at least. The print data generator is configured to generate print data indicative of a state of dot formation in each pixel in response to the print mode selection. The print data generator composes the print data with binary pixel values indicative of presence or absence of the dot formation in each pixel when the specific text print mode is selected, and also composes the print data with multiple pixel values indicative of a state of dot formation in each pixel when the photographic mode is selected. When the specific text print mode is selected, the smoothing processor selects one type of dot from the N types of dots for each pixel in response to the binary pixel value for the each pixel and the binary pixel value for a pixel adjacent to the each pixel.
With this approach, the function of selecting any desired dot type from among a plurality of dot types with different sizes in the area occupied by a single pixel can be adapted both to outline smoothing during text printing and to picture quality enhancement during the printing of photographic images.
In a preferred embodiment of the invention, the print head driver is capable of ejecting ink drops at a plurality of different positions within the pixel area on a print medium. When the specific text print mode is selected, the smoothing processor selects ink-ejected position from the plurality of different positions within the pixel area in response to the binary pixel value for the each pixel and the binary pixel value for a pixel adjacent to the each pixel.
An advantage of this approach is that the outlines of a printed image can be further smoothed by selecting appropriate positions for ejecting ink drops.
In a preferred embodiment of the invention, print mode parameters selectable by the user include a type of print medium. When the specific text print mode is selected, the smoothing processor selects ink-ejected position from the plurality of different positions within the pixel area in response to the type of print medium, the binary pixel value for the each pixel, and the binary pixel value for a pixel adjacent to the each pixel.
The positions in which ink drops are ejected to smooth the outlines sometimes vary with the type of print medium. In such cases, an optimum smoothing process for the selected print medium can be performed by varying the specifics of the smoothing process in accordance with the print medium.
In a preferred embodiment of the invention, print mode parameters selectable by the user include ink color. The smoothing processor is configured to perform the smoothing process for each color of inks when the specific text print mode involving use of color inks is selected.
An advantage of this approach is that the outlines of printed images can be smoothed not only in the case of black text but also in the case of color text.
In a fourth embodiment, there is provided a printing control apparatus for generating print data to be supplied to a printing unit to perform printing by ejecting ink drops from a print head to form dots. The print mode selector allows a user to select one of a plurality of print modes including a specific text print mode suitable for printing text documents, and a photographic print mode suitable for printing photographic images. The print data generator is configured to generate print data containing smoothing command information if the specific text print mode is selected, and also generate the print data devoid of the smoothing command information if the photographic print mode is selected. The smoothing command information commands the printing unit to perform smoothing process for smoothing an outline contained in a printed image.
According to the fourth embodiment of the present invention, print data containing information on smoothing commands are created in accordance with the print mode selected by the user, and because the information on smoothing commands is designed to allow smoothing processs to be performed by a printing unit. This approach also makes it possible to smooth the outlines of printed images by performing smoothing during textual printing while preventing print quality from degrading during photograph printing in the same manner as with the first approach.
In a fifth embodiment, there is provided a printing apparatus for printing by ejecting ink drops from a print head and forming dots in response to supplied printing data, comprising. The smoothing processor is configured to perform a smoothing process if the print data contains smoothing command information, and NOT to perform the smoothing process if the data does not contain the smoothing command information, the smoothing command information indicating that the smoothing process is to be performed to smooth an outline contained in a printed image.
According to the fifth embodiment of the present invention, it is determined whether smoothing is to be performed in accordance with whether information on smoothing commands is contained in the print data supplied, and the information on smoothing commands is included into the print data in accordance with the print mode, allowing this approach to deliver the same effect as the first approach.
The present invention can be realized in various forms such as a method and apparatus for printing, a method and apparatus for producing print data for a printing unit, and a computer program product implementing the above scheme.